1. Field of the Invention
The present invention relates to a linear scale type measuring device in which the relative displacement between a light transmitting linear scale and an index scale relatively opposed to said linear scale is read by use of a light source and a receptor element so as to make measurement.
2. Prior Art
The conventional measuring device of the type described has been such an arrangement that a linear scale made of glass and formed by cold drawing is disposed in a hollow and elongate case in the longitudinal direction, an index scale is disposed in opposed relation to the linear scale, said index scale is mounted through a slider on an arm of a detecting mechanism which is a movable member inserted through an opening formed in the longitudinal direction of said case, a projector element as a light source and a receptor element are provided on said slider, and the relative displacement between the detecting mechanism and the case is detected and measured by the receptor element as the light and darkness formed between the both scales. Additionally, said slider is solidly secured through a screw, etc. to the center portion of a formed wire whose opposite ends are supported by the arm of the detecting mechanism, biased to one side by said formed wire, and probes provided on said slider are brought into abutment with the scale surface of the linear scale and the side surfaces perpendicularly intersecting the scale surface. With this arrangement, the slider is moved under the guidance of the scale surface of the linear scale and said side surfaces, and the scale portion of the linear scale and the scale portion of the index scale are adapted to move in opposed relation to each other.
One such prior art device described above is described in the U.S. Pat. No. 3,833,303.
However, in the conventional linear scale type measuring device as described above, the force keeping the linear scale and the slider having the index scale in pressing contact is provided by a single formed wire supported at opposite ends thereof, and hence, the formed wire is deformed when the slider is moved, the resultant change in the pressingly contacting force may cause one side of the slider to be lifted up relative to the linear scale. If the abutment between the linear scale and the slider becomes unreliable, then the longitudinally striped graduation lines of the linear scale and the longitudinally striped graduation lines of the index scale mounted on the slider come out of parallel, thus resulting in miscount.